The invention relates in general to communication systems and more specifically to an apparatus, system, and method for managing transmission power in a wireless communication system.
Wireless communication systems typically employ power control procedures to maximize the overall performance of the communication system. Power control procedures are particularly advantageous in systems utilizing code division multiple assess (CDMA) techniques since the signals transmitted from user equipment other than the target transmission source appear as noise to the receiver. Accordingly, system performance is improved if the transmission powers of the user equipment are properly managed. In conventional wireless communication systems such as cellular and Universal Mobile Telecommunications Service (UMTS) systems, a base station (node B) periodically transmits power control information to mobile stations (user equipment) indicating whether a mobile station should increase or decrease transmission power. Typically, a base station is referred to as a Node B and mobile stations are referred to as user equipment (UE) in UMTS systems. In addition to the power control commands, the actual transmission power of a UE device depends on the number of channels that are transmitted, the amount of data that is transmitted, and the maximum transmission power of the UE device.
Conventional systems are limited in that transmission power levels determined for a particular set of conditions are not adjusted when the conditions change unless power control commands are received indicating that the power should be changed. Since the power control information is only received periodically, situations arise where a UE device is transmitting data at less than an optimum power level until new power control information is received. In conventional systems, for example, if a UE device is limited by a maximum power limit to transmit at a lower power than authorized by a node B, the UE device scales the transmission power levels of the channels to maintain relative powers between the channels without exceeding the maximum power limit. When the data rate or the number of channels is reduced, the transmission power level remains below the authorized level until new power control information is received. Therefore, the transmission power level of a UE device in a conventional system remains at less than optimum level after a power limited transmission and before a new power control command is received.
Accordingly, there is a need for an apparatus, system, and method for managing transmission power in a wireless communication system.